I have an application where my device will be running from batteries I'm 
running a few fets at ~12 volts (13-11 acceptable range) and logic 
(5V-4.5V range)
Problem is the fets will be pulling several hundred amps from the 
batteries which can cause the input voltage (~18-24V) to sag below 12V 
(and get spikes of 50).
I am happy with a low pass filter on the input side of the power supply 
to knock the tops off the spikes etc but to hold up during the dips I am 
planning on using a super cap on the 12V rail. (probably 13 after a 
diode drop from the regulator). What I don't want to happen however is 
when power is removed (or during really heavy load) for the 12V IC's to 
be left to drift down causing basically a brownout.
What I'm after is something that will when the voltage droops to a set 
point basically short the cap and de-energise the system. Physically 
small is a constraint. An easy to use IC would be nice.
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